CC Chemokine receptor 5 (CCR5) is a coreceptor for the human immunodeficiency virus-1 (HIV-1). CCR5 is expressed by bone marrow-derived cells known to be targets for HIV-1 infection, including a subpopulation of lymphocytes and monocytes/macrophages in blood, primary and secondary lymphoid organs, and noninflamed tissues. An increased number of CCR5-positive mononuclear cells have been found in chronically inflamed tissues, and the number of immunoreactive cells in these tissues was directly associated with a histopathologic correlate of inflammatory severity.